Wireless communication method and wireless communication terminal for spatial reuse of overlapped basic service set

ABSTRACT

The present invention relates to a wireless communication method and a wireless communication terminal for a spatial reuse operation of an overlapping basic service set, and more particularly, to a wireless communication method and a wireless communication terminal for supporting a spatial reuse operation of an overlapping basic service set to efficiently use a wireless resource. To this end, provided are a wireless communication terminal including: a processor; and a communication unit, wherein the processor receives a trigger frame indicating an uplink multi-user transmission, and transmits a trigger-based PHY protocol data unit (PPDU) in response to the received trigger frame, wherein the trigger-based PPDU comprises a spatial reuse parameter for spatial reuse operation of an overlapping basic service set (OBSS) terminal and a wireless communication method using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication method and awireless communication terminal for a spatial reuse operation of anoverlapping basic service set, and more particularly, to a wirelesscommunication method and a wireless communication terminal forsupporting a spatial reuse operation of an overlapping basic service setto efficiently use a wireless resource.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11 g uses the frequenciesof the 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

The present invention has an object to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment as described above.

The present invention has an object to solve an ambiguity of a spatialreuse field identification of an inter-BSS (or an overlapping BSS)terminal receiving a trigger-based PPDU.

The present invention has an object to provide a wireless communicationmethod and a wireless communication terminal in a high densityenvironment including an overlapping basic service set.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, an exemplary embodiment of the present invention provides awireless communication terminal, the terminal including: a processor;and a communication unit, wherein the processor receives a trigger frameindicating an uplink multi-user transmission, and transmits atrigger-based PHY protocol data unit (PPDU) in response to the receivedtrigger frame, wherein the trigger-based PPDU comprises a spatial reuseparameter for spatial reuse operation of an overlapping basic serviceset (OBSS) terminal.

In addition, an exemplary embodiment of the present invention provides awireless communication method of a wireless communication terminal,including: receiving a trigger frame indicating an uplink multi-usertransmission; and transmitting a trigger-based PHY protocol data unit(PPDU) in response to the received trigger frame; wherein thetrigger-based PPDU comprises a spatial reuse parameter for spatial reuseoperation of an overlapping basic service set (OBSS) terminal.

When a total bandwidth thorough which the transmission of thetrigger-based PPDU is performed is a non-contiguous first frequency bandand second frequency band, a spatial reuse parameter for the firstfrequency band and a spatial reuse parameter for the second frequencyband may be set to the same value.

A high efficiency signal field A (HE-SIG-A) of the trigger-based PPDUmay contain a plurality of spatial reuse fields, and the plurality ofspatial reuse fields may carry spatial reuse parameters obtained fromthe trigger frame, and each of the plurality of spatial reuse fields mayindicate a spatial reuse parameter for an individual subbandconstituting the total bandwidth on which the transmission of thetrigger-based PPDU is performed.

The plurality of spatial reuse fields may comprise a first spatial reusefield, a second spatial reuse field, a third spatial reuse field, and afourth spatial reuse field, and when the total bandwidth on which thetransmission of the trigger-based PPDU is performed is a non-contiguousfirst frequency band and second frequency band, the first spatial reusefield and the second spatial reuse field for the first frequency bandmay be respectively set to the same value as the third spatial reusefield and the fourth spatial reuse field for the second frequency band.

When the total bandwidth on which the transmission of the trigger-basedPPDU is performed is less than or equal to a predetermined bandwidth,the spatial reuse field may indicate a spatial reuse parameter for asubband of a first frequency bandwidth, and when the total bandwidth onwhich the transmission of the trigger-based PPDU is performed exceedsthe predetermined bandwidth, the spatial reuse field may indicate aspatial reuse parameter for a subband of a second frequency bandwidthwhich is wider than the first frequency bandwidth.

The spatial reuse parameter may be set based on a transmission power ofa PPDU containing the trigger frame and an acceptable interference levelof a base wireless communication terminal that transmitted the PPDUcontaining the trigger frame.

The spatial reuse operation of the OBSS terminal may comprise anoperation of adjusting a transmission power of the OBSS terminal basedon the spatial reuse parameter.

The operation of adjusting the transmission power may be performed basedon a received signal strength of a PPDU containing the trigger framemeasured by the OBSS terminal and a spatial reuse parameter obtained bythe OBSS terminal.

The transmission power of the OBSS terminal may be set to be lower thana value obtained by subtracting the measured received signal strengthfrom the obtained spatial reuse parameter value.

The OBSS terminal may obtain the spatial reuse parameter from at leastone of the trigger frame and the trigger-based PPDU.

Advantageous Effects

According to an embodiment of the present invention, the ambiguity ofthe spatial reuse field identification of an inter-BSS (or anoverlapping BSS) terminal receiving a trigger-based PPDU can be solved.

In addition, according to an embodiment of the present invention, if thereceived frame is determined as an inter-BSS frame, the spatial reuseoperation can be performed, thereby efficiently using the wirelessresources.

According to an embodiment of the present invention, it is possible toincrease the total resource utilization rate in the contention-basedchannel access system and improve the performance of the wireless LANsystem.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless LAN system according to an embodiment ofthe present invention.

FIG. 2 illustrates a wireless LAN system according to another embodimentof the present invention.

FIG. 3 illustrates a configuration of a station according to anembodiment of the present invention.

FIG. 4 illustrates a configuration of an access point according to anembodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA and an AP seta link.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

FIG. 7 illustrates a channel access method using a spatial reuseoperation according to an embodiment of the present invention.

FIG. 8 illustrates an SR operation of a terminal according to theembodiment of the present invention when a PPDU containing a triggerframe is transmitted in an OBSS.

FIG. 9 illustrates an SR operation of a terminal according to theembodiment of the present invention in more detail when a PPDUcontaining a trigger frame is transmitted in an OBSS.

FIG. 10 illustrates the embodiment in which a terminal performs an SRoperation based on a contention procedure when a PPDU containing atrigger frame is transmitted in an OBSS.

FIG. 11 illustrates an embodiment of an operation in which a terminalsets a NAV when a PPDU containing a trigger frame is transmitted in anOBSS.

FIG. 12 illustrates the embodiment of transmitting a spatial reuseparameter via a trigger frame and a corresponding trigger-based PPDU.

FIG. 13 illustrates a method for signaling spatial reuse fields of atrigger-based PPDU according to the embodiment of the present invention.

FIG. 14 illustrates an embodiment of a method for setting spatial reusefields of a trigger-based PPDU.

FIGS. 15 to 19 illustrate methods for configuring an HE-SIG-A andspatial reuse fields according to the embodiment of the presentinvention.

FIG. 20 illustrates another embodiment of a method for setting spatialreuse fields of a trigger-based PPDU.

FIG. 21 illustrates yet another embodiment of a method for setting andusing spatial reuse fields of a trigger-based PPDU.

FIG. 22 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of a trigger-based PPDU according to a further embodimentof the present invention.

FIG. 23 illustrates a method for signaling spatial reuse fields of atrigger-based PPDU according to another embodiment of the presentinvention.

FIG. 24 illustrates a method for signaling a bandwidth field accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2016-0040551, 10-2016-0074091, 10-2016-0086044 and10-2016-0093813 filed in the Korean Intellectual Property Office and theembodiments and mentioned items described in the respective application,which forms the basis of the priority, shall be included in the DetailedDescription of the present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1 , the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a communication unit andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the communication unit is functionallyconnected with the processor and transmits and receives frames throughthe wireless network for the station. According to the presentinvention, a terminal may be used as a term which includes userequipment (UE).

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense. In the present invention, an AP may also be referredto as a base wireless communication terminal. The base wirelesscommunication terminal may be used as a term which includes an AP, abase station, an eNB (i.e. eNodeB) and a transmission point (TP) in abroad sense. In addition, the base wireless communication terminal mayinclude various types of wireless communication terminals that allocatemedium resources and perform scheduling in communication with aplurality of wireless communication terminals.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2 , duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1 , will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention. As illustrated inFIG. 3 , the station 100 according to the embodiment of the presentinvention may include a processor 110, a communication unit 120, a userinterface unit 140, a display unit 150, and a memory 160.

First, the communication unit 120 transmits and receives a wirelesssignal such as a wireless LAN packet, or the like and may be embedded inthe station 100 or provided as an exterior. According to the embodiment,the communication unit 120 may include at least one communication moduleusing different frequency bands. For example, the communication unit 120may include communication modules having different frequency bands suchas 2.4 GHz, 5 GHz, and 60 GHz. According to an embodiment, the station100 may include a communication module using a frequency band of 6 GHzor more and a communication module using a frequency band of 6 GHz orless. The respective communication modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingcommunication module. The communication unit 120 may operate only onecommunication module at a time or simultaneously operate multiplecommunication modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of communication modules, each communication module may beimplemented by independent elements or a plurality of modules may beintegrated into one chip. In an embodiment of the present invention, thecommunication unit 120 may represent a radio frequency (RF)communication module for processing an RF signal.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the communication unit120, and the like. That is, the processor 110 may be a modem or amodulator/demodulator for modulating and demodulating wireless signalstransmitted to and received from the communication unit 120. Theprocessor 110 controls various operations of wireless signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the communication unit 120 may be implemented whilebeing integrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention. As illustrated inFIG. 4 , the AP 200 according to the embodiment of the present inventionmay include a processor 210, a communication unit 220, and a memory 260.In FIG. 4 , among the components of the AP 200, duplicative descriptionof parts which are the same as or correspond to the components of thestation 100 of FIG. 2 will be omitted.

Referring to FIG. 4 , the AP 200 according to the present inventionincludes the communication unit 220 for operating the BSS in at leastone frequency band. As described in the embodiment of FIG. 3 , thecommunication unit 220 of the AP 200 may also include a plurality ofcommunication modules using different frequency bands. That is, the AP200 according to the embodiment of the present invention may include twoor more communication modules among different frequency bands, forexample, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200 mayinclude a communication module using a frequency band of 6 GHz or moreand a communication module using a frequency band of 6 GHz or less. Therespective communication modules may perform wireless communication withthe station according to a wireless LAN standard of a frequency bandsupported by the corresponding communication module. The communicationunit 220 may operate only one communication module at a time orsimultaneously operate multiple communication modules together accordingto the performance and requirements of the AP 200. In an embodiment ofthe present invention, the communication unit 220 may represent a radiofrequency (RF) communication module for processing an RF signal.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. According to an embodiment, the processor210 may be a modem or a modulator/demodulator for modulating anddemodulating wireless signals transmitted to and received from thecommunication unit 220. The processor 210 controls various operationssuch as wireless signal transmission/reception of the AP 200 accordingto the embodiment of the present invention. A detailed embodimentthereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5 , the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b). In this specification, an association basically means awireless association, but the present invention is not limited thereto,and the association may include both the wireless association and awired association in a broad sense.

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5 , the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the access to the corresponding channel. Such a processis referred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an inter framespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber determined by the corresponding terminal during an interval of anidle state of the channel and a terminal that completely exhausts theslot time(s) attempts to access the corresponding channel. As such, aninterval in which each terminal performs the backoff procedure isreferred to as a contention window interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers, respectively to perform the backoff procedure again.According to an embodiment, a random number newly assigned to eachterminal may be decided within a range (2*CW) which is twice larger thana range (a contention window, CW) of a random number which thecorresponding terminal has previously used. Meanwhile, each terminalattempts the access by performing the backoff procedure again in a nextcontention window interval and in this case, each terminal performs thebackoff procedure from slot time(s) which remained in the previouscontention window interval. By such a method, the respective terminalsthat perform the wireless LAN communication may avoid a mutual collisionfor a specific channel.

Multi-User Transmission

When using orthogonal frequency division multiple access (OFDMA) ormulti-input multi-output (MIMO), one wireless communication terminal cansimultaneously transmit data to a plurality of wireless communicationterminals. Further, one wireless communication terminal cansimultaneously receive data from a plurality of wireless communicationterminals. For example, a downlink multi-user (DL-MU) transmission inwhich an AP simultaneously transmits data to a plurality of STAs, and anuplink multi-user (UL-MU) transmission in which a plurality of STAssimultaneously transmit data to the AP may be performed.

In order to perform the UL-MU transmission, the channel to be used andthe transmission start time of each STA that performs uplinktransmission should be adjusted. According to an embodiment of thepresent invention, the UL-MU transmission process may be managed by theAP. The UL-MU transmission may be performed in response to a triggerframe transmitted by the AP. The trigger frame indicates a UL-MUtransmission of at least one STA. The STAs simultaneously transmituplink data a predetermined IFS time after receiving the trigger frame.The trigger frame may indicate data transmission time point of uplinktransmission STAs and may inform channel (or subchannel) informationallocated to the uplink transmission STAs. When the AP transmits atrigger frame, a plurality of STAs transmit uplink data through eachallocated subcarrier at the time specified by the trigger frame. Afterthe uplink data transmission is completed, the AP transmits an ACK toSTAs that have successfully transmitted uplink data. In this case, theAP may transmit a predetermined multi-STA block ACK (M-BA) as an ACK fora plurality of STAs.

In the non-legacy wireless LAN system, a specific number, for example,26, 52, or 106 tones may be used as a resource unit (RU) for asubchannel-based access in a channel of 20 MHz band. Accordingly, thetrigger frame may indicate identification information of each STAparticipating in the UL-MU transmission and information of the allocatedresource unit. The identification information of the STA includes atleast one of an association ID (AID), a partial AID, and a MAC addressof the STA. Further, the information of the resource unit includes thesize and placement information of the resource unit.

Spatial Reuse Operation

FIG. 7 illustrates a channel access method using a spatial reuse (SR)operation according to an embodiment of the present invention. Due tothe spread of mobile devices and the spread of wireless communicationsystems, terminals are increasingly communicating in a denseenvironment. In particular, the number of cases where a terminalcommunicates in an environment in which a plurality of BSSs areoverlapped is increasing. When a plurality of BSSs are overlapped,communication efficiency of the terminal may be degraded due tointerference with other terminals. In particular, if a frequency band isused through a contention procedure, the terminal may not be able tosecure even a transmission opportunity due to interference with otherterminals. To solve this problem, the terminal may perform the SRoperation.

More specifically, the terminal may determine whether a frame is anintra-BSS frame or an inter-BSS frame based on information foridentifying a BSS of a received frame. The information for identifying aBSS includes at least one of a BSS color, a partial BSS color, a partialAID, or a MAC address. In the embodiment of the present invention, thenon-legacy terminal may refer to a terminal that complies with the nextgeneration wireless LAN standard (i.e., IEEE 802.11ax). Also, theintra-BSS frame indicates a frame transmitted from a terminal belongingto the same BSS, and the inter-BSS frame indicates a frame transmittedfrom a terminal belonging to an overlapping BSS (OBSS) or another BSS.

According to the embodiment of the present invention, the non-legacyterminal may perform different operations depending on whether thereceived frame is an intra-BSS frame. That is, when the received frameis determined as an intra-BSS frame, the terminal may perform the firstoperation. In addition, when the received frame is determined as aninter-BSS frame, the terminal may perform the second operation differentfrom the first operation. According to an embodiment, the secondoperation performed by the terminal when the received frame isdetermined as an inter-BSS frame may be the SR operation. According tothe embodiment of the present invention, the first operation and thesecond operation may be set in various ways.

According to an embodiment, the terminal may perform channel accessbased on different thresholds depending on whether the received frame isan intra-BSS frame. More specifically, when the received frame isdetermined as an intra-BSS frame, the terminal accesses the channelbased on the first CCA threshold (i.e., the first operation). That is,the terminal performs a CCA based on the first CCA threshold value, anddetermines whether the channel is busy based on a result of performingthe CCA. On the other hand, when the received frame is determined as aninter-BSS frame, the terminal may access the channel based on the secondCCA threshold value (i.e., the second operation, or SR operation), whichis distinct from the first CCA threshold value. That is, the terminaldetermines whether the channel is busy based on both the first CCAthreshold value and the second CCA threshold value. According to theembodiment of the present invention, the second CCA threshold value isan OBSS PD level set for determining whether a channel is busy accordingto a received signal strength of an inter-BSS frame. In this case, thesecond CCA threshold value may have a value equal to or larger than thefirst CCA threshold value.

According to another embodiment of the present invention, the terminalmay adjust a transmission power of a PHY protocol data unit (PPDU)transmitted by the terminal according to whether the received frame isan intra-BSS frame. More specifically, when the received frame isdetermined as an inter-BSS frame, the terminal may adjust thetransmission power of the PPDU based on the SR parameter extracted fromthe received frame (i.e., the second operation, or SR operation).According to an embodiment, the terminal may increase the transmissionpower based on the SR parameter extracted from the received frame.According to the embodiment of the present invention, the non-legacyframe may contain an SR field for SR operation of OBSS terminals, andspecific embodiments thereof will be described later. On the other hand,when the received frame is determined as an intra-BSS frame, theterminal does not perform the transmission power adjustment based on theSR parameter.

Referring to FIG. 7 , the transmitted non-legacy frames 310 and 320 maycontain information (i.e., information indicating whether the SR isallowed) indicating whether the SR operation for the corresponding PPDUis allowed. According to an embodiment, the information indicatingwhether the SR is allowed may be represented through a predeterminedindex of the SR field. For example, if the value of the SR field is 0(i.e., if all bit values of the SR field are 0), it may indicate thatthe SR operation is not allowed. In the embodiment of FIG. 7 ,information, contained in the received first frame 310, indicatingwhether the SR is allowed indicates that the SR operation for thecorresponding PPDU is allowed. In addition, information, contained inthe received second frame 320, indicating whether the SR is allowedindicates that the SR operation for the corresponding PPDU is notallowed. In this case, it is assumed that both of the received firstframe 310 and the received second frame 320 are inter-BSS frames.

The terminal receiving the first frame 310 determines whether thereceived frame 310 is an intra-BSS frame or an inter-BSS frame. Inaddition, the terminal checks information indicating whether the SR isallowed in the received frame 310. In this case, the received frame 310is determined as an inter-BSS frame, and the information indicatingwhether the SR is allowed indicates that the SR operation for thecorresponding PPDU is allowed. Accordingly, the terminal may perform theSR operations according to the above-described embodiments. That is, theterminal may determine whether the channel is busy based on both thefirst CCA threshold value and the second CCA threshold value. Inaddition, the terminal may adjust the transmission power based on the SRparameter extracted from the received frame 310.

Meanwhile, the terminal receiving the second frame 320 determineswhether the received frame 320 is an intra-BSS frame or an inter-BSSframe. In addition, the terminal checks information indicating whetherthe SR is allowed in the received frame 320. In this case, the receivedframe 320 is determined as an inter-BSS frame, and the informationindicating whether the SR is allowed indicates that the SR operation forthe corresponding PPDU is not allowed. Therefore, the terminal does notperform the SR operations according to the above-described embodiment.That is, although the received frame 320 is determined as an inter-BSSframe, the terminal accesses the channel based on the first CCAthreshold value. In addition, the terminal does not perform thetransmission power adjustment based on the SR parameter extracted fromthe received frame 320.

According to a further embodiment of the present invention, theinformation indicating whether the SR is allowed may be transmittedthrough a frame of the legacy format. By containing the informationindicating whether the SR is allowed in the frame of the legacy format,the AP can protect the transmitted legacy frame from SR operations ofthe non-legacy terminals. According to an embodiment, the informationindicating whether the SR is allowed may be transmitted via anL-preamble. For example, reserved bit(s) of an L-SIG of the L-preamblemay indicate whether the SR is allowed. Alternatively, guardsub-carrier(s) of the L-SIG of the L-preamble may carry the informationindicating whether the SR is allowed.

According to another embodiment, the information indicating whether theSR is allowed may be transmitted via a VHT-preamble. For example,reserved bit(s) of a VHT-SIG-A1 or VHT-SIG-A2 of the VHT-preamble mayindicate whether the SR is allowed. Alternatively, guard subcarrier(s)of the VHT-SIG-A1 or VHT-SIG-A2 of the VHT-preamble may carry theinformation indicating whether the SR is allowed. According to yetanother embodiment, the information indicating whether the SR is allowedmay be transmitted via an HT-preamble. For example, reserved bit(s) ofthe HT-preamble may indicate whether the SR is allowed. Alternatively,guard subcarrier(s) of the HT-preamble may carry the informationindicating whether the SR is allowed. According to still anotherembodiment of the present invention, the information indicating whetherthe SR is allowed may be transmitted via a MAC header.

FIG. 8 illustrates an SR operation of a terminal according to theembodiment of the present invention when a PPDU containing a triggerframe is transmitted in an OBSS. In the embodiment of FIG. 8 , BSS1includes STA1 and STA2. In this case, STA1 is a non-AP STA and STA2 isan AP. Also, BSS2 includes STA3 and STA4. In this case, STA3 is a non-APSTA and STA4 is an AP. In the embodiment of FIG. 8 , STA2 transmits atrigger frame (or a PPDU containing a trigger frame) to STA1, and STA1transmits an uplink PPDU in response thereto. The uplink PPDUtransmitted by STA1 transmits may be a trigger-based PPDU. Meanwhile,STA3 of BSS2 intends to transmit a PPDU to STA4. Prior to transmissionof the PPDU, STA3 may receive the trigger frame transmitted by the STA2and/or the trigger-based PPDU transmitted by the STA1. In this case,STA3 may obtain an SR parameter from at least one of the trigger frameand the corresponding trigger-based PPDU.

According to the embodiment of the present invention, an AP may signalinformation of at least one of an acceptable interference level of theAP and a transmission power of a PPDU containing a trigger frame whentransmitting the trigger frame. More specifically, the AP may carry anSR parameter (hereinafter, SRP) through a trigger frame. According tothe embodiment of the present invention, the SRP may be set as follows.

$\begin{matrix}\text{SRP = TXPWR\_AP + Acceptable Receiver Interference Level\_AP} & \text{­­­[Equation 1]}\end{matrix}$

Herein, ‘TXPWR_AP’ denotes the transmission power of the PPDU containingthe trigger frame. In addition, ‘Acceptable Receiver InterferenceLevel_AP’ denotes the level of interference that an AP transmitting thetrigger frame can tolerate, that is, an acceptable interference level.The acceptable interference level may indicate the level of interferencethat the AP can tolerate when a trigger-based PPDU in response to thetrigger frame transmitted by the AP is received. As such, the SRP may bedetermined based on the transmission power of the PPDU containing thetrigger frame and the acceptable interference level. More specifically,the SRP may be set to the sum of the transmission power of the PPDUcontaining the trigger frame and the acceptable interference level.

According to the embodiment of the present invention, the AP maytransmit the SRP determined by Equation 1 by inserting it into thetrigger frame. According to an embodiment, the SRP may be contained in acommon information field of the trigger frame. The STA receiving thetrigger frame from the AP transmits a multi-user uplink frame, that is,a trigger-based PPDU in response thereto. In this case, the STA maycarry the SRP information obtained from the trigger frame through apredetermined field of the trigger-based PPDU. According to anembodiment, the SRP information may be contained in the SR field ofHE-SIG-A of the trigger-based PPDU.

Meanwhile, the terminal receiving the trigger frame transmitted from theOBSS may perform the SR operation based on the obtained SRP. In thiscase, the SRP may be obtained from at least one of the trigger frame andthe corresponding trigger-based PPDU. According to an embodiment, theterminal may adjust the transmission power of the PPDU based on the SRPas follows.

$\begin{matrix}\text{TXPWR\_STA < SRP - RSSI\_TriggerFrame\_at\_STA} & \text{­­­[Equation 2]}\end{matrix}$

Herein, ‘TXPWR_STA’ denotes the transmission power of the PPDU to betransmitted by the terminal. Also, ‘RSSI_TriggerFrame_at_STA’ denotesthe received signal strength of the PPDU containing the trigger framemeasured by the terminal. That is, the transmission power of theterminal is set to be lower than the value obtained by subtracting thereceived signal strength of the PPDU containing the trigger frame fromthe obtained SRP value. According to the embodiment of the presentinvention, the terminal may transmit the PPDU with the transmissionpower ‘TXPWR_STA’ set according to Equation 2. Alternatively, theterminal may transmit the PPDU only when the intended transmission power‘TXPWR_STA’ of the terminal is less than the value obtained bysubtracting the received signal strength of the PPDU containing thetrigger frame from the obtained SRP value, as in Equation 2.

According to the embodiment of FIG. 8 , the STA2 transmits the SRP byinserting it into the trigger frame. In addition, STA1 transmits thetrigger-based PPDU in response to the received trigger frame. In thiscase, STA1 may insert the SRP into a predetermined field of thetrigger-based PPDU. STA3 measures the received signal strength of thePPDU containing the trigger frame transmitted by the STA2. In addition,STA3 may obtain the SRP from at least one of the trigger frametransmitted by the STA2 and the trigger-based PPDU transmitted by theSTA1. According to the embodiment the present invention, when thetransmission power value of a PPDU to be transmitted to STA4 by STA3 islower than the transmission power determined by the Equation 2, STA3 maytransmit the PPDU to STA4.

The magnitudes of the transmission power and the interference may bevalues normalized to the 20 MHz frequency bandwidth. For example, TXPWR= power -10*log(BW/20 MHz). In this case, BW denotes the totaltransmission bandwidth. Thus, the SRP may be a normalized value in the20 MHz frequency bandwidth. Accordingly, the terminal may scale thetransmission power value of the PPDU to be transmitted according to thefrequency bandwidth used by the PPDU to be transmitted to apply theabove-described equation.

When a terminal receives a radio signal, the terminal may separatelyprocess the received signal in a physical layer and a MAC layer. In thiscase, the interface between the physical layer and the MAC layer isreferred to as a primitive. In addition, the operation of the physicallayer of the terminal can be performed by a PHY layer management entity(PLME). In addition, the operation of the MAC layer of the terminal canbe performed by a MAC layer management entity (MLME). In this case, forthe above-described embodiments, the RXVECTOR of the primitive maycontain at least one of SRP (or SR field value), transmissionopportunity (TXOP) duration, or a BSS color.

FIG. 9 illustrates an SR operation of a terminal according to theembodiment of the present invention in more detail when a PPDUcontaining a trigger frame is transmitted in an OBSS. As described withreference to FIG. 8 , the terminal may transmit a PPDU according to theSR operation based on the received signal strength of the PPDUcontaining the trigger frame transmitted from the OBSS and the value ofthe obtained SRP. Specifically, the terminal may transmit the PPDU byadjusting the transmission power based on the received signal strengthof the PPDU containing the trigger frame transmitted from the OBSS andthe value of the SRP indicated by the trigger frame and/or thetrigger-based PPDU.

More specifically, the terminal may adjust the transmission power of thePPDU to be transmitted to satisfy Equation 2 as described above. In thiscase, the terminal may access the channel and transmit the PPDU byadjusting the transmission power at the time of obtaining the SRP value.According to another embodiment, the terminal may start transmission ofthe PPDU by adjusting the transmission power at the end of thetransmission of the PPDU containing the trigger frame transmitted fromthe OBSS. However, when the PPDU containing the trigger frame is alegacy PPDU, the terminal may decode the MAC frame of the correspondingPPDU to determine whether the PPDU contains the trigger frame. Also, ifthe BSS indicated by the signaling field of the PPDU is different fromthe BSS indicated by the address field of the MAC header, the terminalmay decode the MAC frame of the corresponding PPDU. At this time, theterminal may obtain the SRP value from the trigger frame.

In the embodiment of FIG. 9 , it is illustrated that the terminaltransmits the PPDU by adjusting the transmission power at the end of thetransmission of the PPDU containing the trigger frame transmitted fromthe OBSS. According to another specific embodiment, when the PPDUcontaining the trigger frame is a legacy PPDU, the terminal may transmitthe PPDU by adjusting the transmission power at the time when theterminal checks that the PPDU is the trigger frame transmitted from theOBSS. In these embodiments, the terminal may transmit the PPDU based onthe SR operation at a time point earlier than the embodiment describedwith reference to FIG. 8 .

FIG. 10 illustrates the embodiment in which a terminal performs an SRoperation based on a contention procedure when a PPDU containing atrigger frame is transmitted in an OBSS. As described above, during thetransmission procedure of the trigger frame and the correspondingtrigger-based PPDU in the OBSS, the terminal can transmit a PPDU basedon the SR operation. Specifically, the terminal may transmit the PPDUaccording to the condition of Equation 2. That is, the terminal maytransmit the PPDU by adjusting the transmission power according toEquation 2.

Meanwhile, one or more terminals may transmit a PPDU based on the SRoperation during the transmission procedures in the OBSS. However, whena plurality of terminals transmit PPDUs based on the SR operation, acollision may occur between transmissions of different terminals.Further, when a plurality of terminals transmit PPDUs, interferenceexceeding the magnitude of interference that can be tolerated by theOBSS access point may occur.

In the embodiment of FIG. 10 , BSS1 includes STA1 and STA2. In thiscase, STA1 is a non-AP STA and STA2 is an AP. Also, BSS2 includes STA3,STA4, and STA5. In this case, STA3 is a non-AP STA, STA4 is an AP, andSTA5 is a non-AP STA. In addition, BSS3 includes STA6, and STA6 is anon-AP STA. In the embodiment of FIG. 10 , STA2 transmits a triggerframe (or PPDU containing a trigger frame) to STA1, and STA1 transmitsan uplink PPDU in response thereto. The uplink PPDU transmitted by STA1may be a trigger-based PPDU.

In the embodiment of FIG. 10 , when at least two of STA3 to STA6transmit PPDUs at the same time, a collision may occur. In addition,when at least two of STA3 to STA6 transmit PPDUs at the same time,interference exceeding the magnitude of interference that can betolerated by STA2 may occur. Accordingly, STA2 may not receive the PPDUfrom STA1. In order to solve this problem, when the PPDU transmission isperformed based on the SR operation, the terminal may access the channelby performing a backoff procedure.

Referring to FIG. 10 , if the PPDU is transmitted based on the SRoperation, the terminal may perform the backoff procedure describedabove. In this case, the terminal may use the backoff counter used whenaccessing the channel through the DCF and the EDCAF as the backoffcounter value of the corresponding backoff procedure. According to anembodiment of the present invention, in order to determine whether thechannel is idle in the backoff procedure, the terminal may use energydetect (ED). According to another embodiment of the present invention,the terminal may determine whether the channel is idle according towhether a PPDU having a signal strength higher than a threshold value isreceived. In this case, the threshold value may be a value larger thanthe existing minimum receive sensitivity. For example, the terminal maydetermine whether the channel is idle based on the above-described OBSSPD level. According to the embodiment of the present invention, the OBSSPD level used by the terminal in the SR operation may be set to a largevalue without any limitation. For example, the OBSS PD level used in theSR operation may be set to a predetermined value below the infinitevalue. During the transmission of the trigger-based PPDU of the OBSS,the terminal may perform the SR operation using the set OBSS PD level.

FIG. 11 illustrates an embodiment of an operation in which a terminalsets a NAV when a PPDU containing a trigger frame is transmitted in anOBSS. If the PPDU containing the trigger frame is transmitted in theOBSS and the terminal can transmit a PPDU based on the SR operation, theterminal may not set a NAV according to the trigger frame (or the PPDUcontaining the trigger frame). In addition, if the terminal fails toreceive the PPDU containing the trigger frame transmitted from the OBSS,the terminal cannot set the NAV according to the trigger frame.

When the terminal receives the trigger-based PPDU transmitted from theOBSS, the terminal can transmit the PPDU based on the SR operation as inthe above-described embodiments. However, if the conditions fortransmitting the PPDU based on the SR operation are not satisfied, theterminal may set a NAV based on the signaling field of the trigger-basedPPDU. In this case, the signaling field may be a TXOP duration field ofthe HE-SIG-A field. If the conditions for transmitting the PPDU based onthe SR operation are not satisfied, the terminal may perform a CCA byusing a value less than or equal to the first CCA threshold rather thanthe above-set OBSS PD level (i.e., the second CCA threshold) during thetransmission of the trigger-based PPDU in the OBSS. This is because thePPDU transmission based on the SR operation of the terminal can giveinterference more than the magnitude of the interference that can betolerated by the AP of the OBSS that will receive the trigger-basedPPDU. Meanwhile, in the embodiment of FIG. 11 , STA2 receives the legacypreamble of the trigger-based PPDU transmitted in the OBSS, but may notreceive the non-legacy signaling field. In this case, the STA2 mayperform the CCA based on the minimum receive sensitivity.

According to a further embodiment of the present invention, if theinformation for determining whether the condition for transmitting aPPDU based on the SR operation is satisfied is not sufficient, theterminal may not perform the PPDU transmission based on the SRoperation. In this case, the terminal may perform the CCA by using thefirst CCA threshold rather than the OBSS PD level (i.e., the second CCAthreshold) during the transmission of the trigger-based PPDU in theOBSS. In this case, the case that the information for determiningwhether the condition for transmitting a PPDU based on the SR operationis satisfied is not sufficient includes a case that the terminal failsto receive the trigger frame.

FIG. 12 illustrates the embodiment of transmitting a spatial reuseparameter via a trigger frame and a corresponding trigger-based PPDU. Inthe embodiment of FIG. 12 , the AP transmits a trigger frame (or a PPDUcontaining a trigger frame), and the receiving STAs transmit atrigger-based PPDU.

As described above, the AP may transmit the SRP determined by Equation 1by inserting it into the trigger frame. According to an embodiment, theSRP may be contained in the common information field of the triggerframe. The STA receiving the trigger frame from the AP transmits atrigger-based PPDU in response thereto. In this case, the STA may carrythe SRP information obtained from the trigger frame through apredetermined field of the trigger-based PPDU. According to anembodiment, the SRP information may be contained in the SR field ofHE-SIG-A of the trigger-based PPDU. That is, the SR field of thetrigger-based PPDU may carry the SRP obtained from the trigger frame.

According to the embodiment of the present invention, the HE-SIG-A ofthe trigger-based PPDU may contain a plurality of SR fields. Theplurality of SR fields carry the SRP obtained from the trigger frame. Inthis case, each of the plurality of SR fields indicates an SRP for anindividual subband constituting the total bandwidth on which thetrigger-based PPDU(s) are transmitted. The total bandwidth on which thetrigger-based PPDU(s) are transmitted may be indicated by a bandwidthfield of the HE-SIG-A of the trigger-based PPDU. Referring to FIG. 12 ,HE-SIG-A of the trigger-based PPDU may contain N SR fields. Each of theN SR fields may indicate an SRP for an individual subband in units of 20MHz or 40 MHz. According to the embodiment of the present invention, Nmay be set to 4. That is, the plurality of SR fields may include a firstSR field, a second SR field, a third SR field, and a fourth SR field.However, the present invention is not limited thereto. According to anembodiment, the plurality of SR fields may indicate SRPs for differentsubbands, respectively. However, according to the embodiment of thepresent invention, under certain conditions, at least some of theplurality of SR fields may be set to have the same value. A specificembodiment will be described later.

HE-SIG-A of the PPDU in an HE format signals the same information inunits of 20 MHz bandwidth. That is, the plurality of SR fields of theHE-SIG-A may be duplicated in units of 20 MHz bandwidth, and may becarried through the total bandwidth in which the trigger-based PPDU istransmitted. Therefore, the terminal receiving the trigger-based PPDUcan detect N SR fields corresponding to each subband.

The physical band on which the trigger-based PPDU is transmitted may beidentified through various information or a combination thereof.According to an embodiment, the physical band on which the trigger-basedPPDU is transmitted may be identified based on bandwidth fieldinformation and operating class information. The bandwidth field of theHE-SIG-A of the trigger-based PPDU indicates the total bandwidth onwhich the trigger-based PPDU(s) are transmitted. In addition, theoperating class information may include information on which band aparticular band can combine with to configure a wideband channel.Accordingly, the terminal receiving the trigger-based PPDU may identifythe order of the subband, in which the corresponding PPDU is received,among the total bandwidth based on the bandwidth field information andthe operating class information extracted from the received PPDU. Inaddition, the terminal receiving the trigger-based PPDU may identify theSR field for the band in which the corresponding PPDU is received amongthe plurality of SR fields based on the bandwidth field information andthe operating class information. Meanwhile, although a method ofidentifying the physical band on which the trigger-based PPDU istransmitted has been described above, the physical band on which thePPDU in an HE format is transmitted can also be identified in the samemanner.

According to another embodiment of the present invention, the PPDU in anHE format may separately signal the physical band information on whichthe corresponding PPDU is transmitted. For example, the HE-SIG-A of theHE PPDU may contain physical band information on which the PPDU istransmitted. More specifically, the HE-SIG-A may indicate one or morefrequency information indicating the physical band information on whichthe corresponding PPDU is transmitted. For example, the HE-SIG-A mayindicate the start frequency index of the band on which the PPDU istransmitted. In addition, when the total bandwidth on which the PPDU istransmitted is 80+80 MHz or 160 MHz, the HE-SIG-A may indicate at leasttwo frequency indices. According to yet another embodiment of thepresent invention, the PPDU in an HE format may signal center frequencyinformation of the physical band on which the corresponding PPDU istransmitted. In addition, when the total bandwidth on which the PPDU istransmitted is 80+80 MHz or 160 MHz, at least two center frequencyinformation for the physical band on which the PPDU is transmitted maybe signaled.

According to an embodiment of the present invention, the trigger-basedPPDU may signal channel information corresponding to each of theplurality of SR fields of the HE-SIG-A. In this case, the channelinformation includes information on at least one of a channel number, afrequency of the channel, and a center frequency of the channel. Thechannel information to be signaled may be sequentially matched to theplurality of SR fields. If the total bandwidth on which thetrigger-based PPDU(s) are transmitted is 80+80 MHz or 160 MHz, the totalbandwidth may be divided into a first frequency band and a secondfrequency band in units of 80 MHz. According to an embodiment of thepresent invention, the trigger-based PPDU may signal channel informationcorresponding to SR fields for the first frequency band and the secondfrequency band, respectively. According to another embodiment, thetrigger-based PPDU may signal channel information corresponding to SRfields for either the first frequency band or the second frequency band.In this case, only the channel information corresponding to the SRfields for either the first frequency band or the second frequency bandmay be explicitly indicated. The terminal receiving the trigger-basedPPDU may identify the SR field for the band on which the PPDU isreceived among the plurality of SR fields according to whether the bandon which the corresponding PPDU is received is the band in which thechannel information is explicitly indicated.

According to an embodiment of the present invention, the SR field may beadjusted according to the total bandwidth on which the trigger-basedPPDU(s) are transmitted. According to an embodiment, when the totalbandwidth indicated by the bandwidth field exceeds a predeterminedbandwidth, the number of the plurality of SR fields contained in theHE-SIG-A may be increased. According to another embodiment, when thetotal bandwidth indicated by the bandwidth field exceeds thepredetermined bandwidth, the frequency bandwidth corresponding to eachSR field may be increased. More specifically, when the total bandwidthindicated by the bandwidth field is less than or equal to thepredetermined bandwidth, the SR field may indicate an SRP for a subbandof a first frequency bandwidth. However, when the total bandwidthindicated by the bandwidth field exceeds the predetermined bandwidth,the SR field may indicate an SRP for a subband of a second frequencybandwidth that is wider than the first frequency bandwidth. For example,when the total bandwidth indicated by the bandwidth field is 20 MHz, 40MHz, or 80 MHz, then the SR field may indicate an SRP for a subband of20 MHz bandwidth. However, when the total bandwidth indicated by thebandwidth field is 80+80 MHz or 160 MHz, then the SR field may indicatean SRP for a subband of 40 MHz bandwidth.

FIG. 13 illustrates a method for signaling spatial reuse fields of atrigger-based PPDU according to the embodiment of the present invention.Referring to FIG. 13 , HE-SIG-A of the trigger-based PPDU may contain aplurality of SR fields. According to the embodiment of the presentinvention, the HE-SIG-A of the trigger-based PPDU may contain four SRfields. That is, HE-SIG-A contains a first SR field, a second SR field,a third SR field, and a fourth SR field. Also, each SR field may consistof 4 bits. Each of the SR fields may indicate an SRP for an individualsubband in units of 20 MHz or 40 MHz.

First, when the total bandwidth on which the trigger-based PPDU(s) aretransmitted is 20 MHz, the first SR field indicates an SRP for thecorresponding 20 MHz band. In addition, the second SR field, the thirdSR field, and the fourth SR field are set to the same value as the firstSR field.

Next, when the total bandwidth on which the trigger-based PPDU(s) aretransmitted is 40 MHz, the first SR field indicates an SRP for the first20 MHz band and the second SR field indicates an SRP for the second 20MHz band. In addition, the third SR field is set to the same value asthe first SR field, and the fourth SR field is set to the same value asthe second SR field. In this case, the first 20 MHz band and the second20 MHz band constitute the total bandwidth of 40 MHz on which thetrigger-based PPDU(s) are transmitted.

Next, when the total bandwidth on which the trigger-based PPDU(s) aretransmitted is 80 MHz, the first SR field indicates an SRP for the first20 MHz band, the second SR field indicates an SRP for the second 20 MHzband, the third SR field indicates an SRP for the third 20 MHz band, andthe fourth SR field indicates an SRP for the fourth 20 MHz band. In thiscase, the first 20 MHz band to the fourth 20 MHz band constitute thetotal bandwidth of 80 MHz on which the trigger-based PPDU(s) aretransmitted.

Meanwhile, when the total bandwidth on which the trigger-based PPDU(s)are transmitted is 160 MHz, the first SR field indicates an SRP for thefirst 40 MHz band, the second SR field indicates an SRP for the second40 MHz band, the third SR field indicates an SRP for the third 40 MHzband, and the fourth SR field indicates an SRP for the fourth 40 MHzband. In this case, the first 40 MHz band to the fourth 40 MHz bandconstitute the total bandwidth 160 MHz on which the trigger-basedPPDU(s) are transmitted.

According to the embodiment of the present invention, the plurality ofSR fields may indicate SRPs for a plurality of subbands in physicalfrequency order. According to an embodiment, the plurality of SR fieldsmay indicate SRPs for a plurality of subbands in ascending order of thephysical frequency. That is, the first SR field may indicate an SRP forthe lowest frequency subband, and the fourth SR field may indicate anSRP for the highest frequency subband. According to another embodiment,the plurality of SR fields may indicate SRPs for a plurality of subbandsin descending order of the physical frequency. That is, the first SRfield may indicate an SRP for the highest frequency subband, and thefourth SR field may indicate an SRP for the lowest frequency subband.

FIG. 14 illustrates an embodiment of a method for setting spatial reusefields of a trigger-based PPDU. As described above, when the totalbandwidth on which the trigger-based PPDU(s) are transmitted is 160 MHz(or 80+80 MHz), each SR field of the trigger-based PPDU may indicate anSRP for an individual subband in units of 40 MHz. Therefore, a methodfor setting SRPs for individual subbands in units of 40 MHz is needed.

According to the embodiment of FIG. 14 , the SR field x for the x-th 40MHz band may be determined by reflecting an SRP for the 20 MHz channelxa and an SRP for the 20 MHz channel xb (where x = 1, 2, 3 or 4). If theSR field indicates an SRP for a subband in units of 40 MHz, theresolution of information for the individual subbands is reduced. Forexample, if the SR field x is determined by normalizing the SRP forchannel xa and the SRP for channel xb, and the situation of channel xaand channel xb is different, then an interference which exceeds theacceptable interference level may occur at a channel in a bad conditionamong the two channels. Therefore, according to the embodiment of thepresent invention, the SR field for the 40 MHz band may be determinedbased on a conservative value among the SRPs for the 20 MHz subbandsconstituting the corresponding band.

According to an embodiment of the present invention, the SR field x forthe x-th 40 MHz band may be determined as shown in Equation 3.

$\begin{matrix}\begin{array}{l}{\text{SRP\_x = 2*min}\left( \text{SRP\_xa, SRP\_xb} \right)} \\{\mspace{6mu}\mspace{6mu}\text{where}} \\\text{SRP\_xa =} \\\text{TX PWR\_AP, xa + Acceptable Receiver Interference Level\_AP, xa} \\\text{SRP\_xb =} \\\text{TX PWR\_AP, xb + Acceptable Receiver Interference Level\_AP, xb}\end{array} & \text{­­­[Equation 3]}\end{matrix}$

Herein, ‘SRP x’ denotes the value of the SR field x, that is, the x-thSRP. Also, ‘SRP_xa’ and ‘SRP_xb’ denote SRPs for the first 20 MHz bandand the second 20 MHz band, respectively, constituting the x-th 40 MHzband. ‘SRP_xa’ may be set to the sum of the transmission power ‘TX PWRAP, xa’ of the PPDU containing the trigger frame on channel xa and theacceptable interference level ‘Acceptable Receiver InterferenceLevel_AP, xa’ in channel xa. Also, ‘SRP_xb’ may be set to the sum of thetransmission power ‘TX PWR AP, xb’ of the PPDU containing the triggerframe on channel xb and the acceptable interference level ‘AcceptableReceiver Interference Level _AP, xb’ in channel xb. That is, accordingto the embodiment of Equation 3, the SR field x may be set to twice theminimum value of ‘SRP_xa’ and ‘SRP_xb’ for the respective 20 MHz band.

According to another embodiment of the present invention, the SR field xfor the x-th 40 MHz band may be determined as shown in Equation 4.

$\begin{matrix}\begin{array}{l}\text{SRP\_x =} \\\text{TX PWR\_AP, x + Acceptable Receiver Interference Level\_AP, x} \\{\mspace{6mu}\mspace{6mu}\text{where}} \\{\text{TX PWR\_AP, x = 2*min}\left( \text{TX PWR\_AP, xa,TX PWR\_AP, xb} \right)} \\\text{Acceptable Receiver Interference Level\_AP, x =} \\{\text{2*min}\left( \text{Acceptable Receiver Interference Level\_AP, xa,} \right)} \\\left( {\quad\quad\mspace{6mu}\mspace{6mu}\mspace{6mu}\mspace{6mu}\text{Acceptable Receiver Interference Level\_AP, xb}} \right)\end{array} & \text{­­­[Equation 4]}\end{matrix}$

Referring to Equation 4, ‘SRP x’ may be set to the sum of thetransmission power ‘TX PWR AP, x’ of the PPDU containing the triggerframe in channel x and the tolerable interference level ‘AcceptableReceiver Interference Level _AP, x’. In this case, ‘TX PWR_AP, x’ may beset to twice the minimum value of ‘TX PWR_AP_xa’ and ‘TX_PWR_AP_xb’. Inaddition, ‘Acceptable Receiver Interference Level _AP, x’ may be set totwice the minimum value of ‘Acceptable Receiver Interference Level_AP,xa’ and ‘Acceptable Receiver Interference Level_AP, xb’. The definitionof each variable in Equation 4 is as described in Equation 3.

According to yet another embodiment of the present invention, the SRfield x for the x-th 40 MHz band may be determined as shown in Equation5.

$\begin{matrix}\begin{array}{l}{\text{SRP\_x = min}\left( \text{SRP\_xa, SRP\_xb} \right)} \\{\mspace{6mu}\mspace{6mu}\text{where}} \\\text{SRP\_xa =} \\\text{TX PWR\_AP, xa + Acceptable Receiver Interference Level\_AP, xa} \\\text{SRP\_xb =} \\\text{TX PWR\_AP, xb + Acceptable Receiver Interference Level\_AP, xb}\end{array} & \text{­­­[Equation 5]}\end{matrix}$

Referring to Equation 5, ‘SRP_x′ may be set to a minimum value among′SRP_xa’ and ‘SRP_xb’. The calculation method of ‘SRP_xa’ and ‘SRP_xb’and the definition of each variable are as described in Equation 3.According to the embodiment of Equation 5, without performing anoperation of multiplying SRP for the 20 MHz band by 2, the terminal canrecognize in advance that ‘SRP_x’ corresponds to the 20 MHz band.

According to still another embodiment of the present invention, the SRfield x for the x-th 40 MHz band may be determined as shown in Equation6.

$\begin{matrix}\begin{array}{l}\text{SRP\_x =} \\\text{TX PWR\_AP, x + Acceptable Receiver Interference Level\_AP, x} \\{\mspace{6mu}\mspace{6mu}\text{where}} \\{\text{TX PWR\_AP, x = min}\left( \text{TX PWR\_AP, xa,TX PWR\_AP, xb} \right)} \\\text{Acceptable Receiver Interference Level\_AP, x =} \\{\text{min}\left( \text{Acceptable Receiver Interference Level\_AP, xa,} \right)} \\\left( {\quad\quad\text{Acceptable Receiver Interference Level\_AP, xb}} \right)\end{array} & \text{­­­[Equation 6]}\end{matrix}$

Referring to Equation 6, ‘SRP x’ may be set to the sum of ‘TX PWR_AP, x′and ‘Acceptable Receiver Interference Level_AP, x’. In this case, ‘TXPWR AP, x’ may be set to a minimum value among ‘TX PWR_AP_xa’ and‘TX_PWR_AP_xb’. In addition, ‘Acceptable Receiver Interference Level_AP,x’ may be set to a minimum value among ‘Acceptable Receiver InterferenceLevel_AP, xa’ and ‘Acceptable Receiver Interference Level _AP, xb’. Thedefinition of each variable in Equation 6 is as described in Equation 3.According to the embodiment of Equation 6, the terminal can recognize inadvance that ‘SRP_x’ corresponds to the 20 MHz band.

FIGS. 15 to 19 illustrate methods for configuring an HE-SIG-A andspatial reuse fields according to the embodiment of the presentinvention. In each of the embodiments shown in FIGS. 15 to 19 ,duplicative description of parts which are the same as or correspond tothe embodiments of the previous drawings will be omitted.

As described above, the HE-SIG-A of the trigger-based PPDU may containfour SR fields. When the total bandwidth on which the trigger-basedPPDU(s) are transmitted is 160 MHz (or 80+80 MHz), each of the SR fieldsmay indicate an SRP for an individual subband in units of 40 MHz. Inthis case, the trigger-based PPDU may be transmitted on at least one ofthe primary 80 MHz channel (hereinafter, P80 channel) and the secondary80 MHz channel (hereinafter, S80 channel). However, an OBSS terminalreceiving the trigger-based PPDU cannot know the frequency bandconfiguration of the BSS in which the corresponding PPDU is transmitted.More specifically, when the total bandwidth on which the trigger-basedPPDU(s) are transmitted is 80+80 MHz, the OBSS terminal may not be ableto identify the physical band of the P80 channel and the S80 channelconstituting the total bandwidth. Therefore, the OBSS terminal receivingthe PPDU cannot identify which frequency band the SR fields of thecorresponding PPDU are for. Also, the OBSS terminal cannot identifywhich SR field among the SR fields is for the subband on which thecorresponding PPDU is received. Therefore, there is a need for a methodfor resolving the ambiguity of the SR field identification of the OBSSterminals receiving the trigger-based PPDU.

FIG. 15 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of the trigger-based PPDU according to an embodiment of thepresent invention. According to the embodiment of FIG. 15 , the HE-SIG-Aof a PPDU in an HE format may contain a location field. The locationfield may indicate either the first frequency band or the secondfrequency band constituting the total bandwidth. For example, when thetotal bandwidth on which the trigger-based PPDUs 410 and 420 aretransmitted is 80+80 MHz, then the location field of the HE-SIG-A mayindicate either the first 80 MHz frequency band or the second 80 MHzfrequency band. According to the embodiment of the present invention,the first SR field and the second SR field of the HE-SIG-A may indicatean SRP for the first frequency band, and the third SR field and thefourth SR field of the HE-SIG-A may indicate an SRP for the secondfrequency band.

The first frequency band and the second frequency band can be classifiedby various methods. According to an embodiment, the first frequency bandmay be a low frequency band and the second frequency band may be a highfrequency band. According to another embodiment, the first frequencyband may be a high frequency band and the second frequency band may be alow frequency band. According to yet another embodiment, the firstfrequency band may be a band of the P80 channel and the second frequencyband may be a band of the S80 channel. In the embodiment of FIG. 15 ,the trigger-based PPDU 410 transmitted on the first frequency band mayset the location field to 1 (or 0) and the trigger-based PPDU 420transmitted on the second frequency band may set the location field to 0(or 1). In the embodiments of the present invention, the first frequencyband and the second frequency band indicate different 80 MHz bands, butthe present invention is not limited thereto.

An OBSS terminal receiving the trigger-based PPDUs 410, 420 may identifyan SRP for the subband on which the corresponding PPDUs 410, 420 isreceived based on the location field information of the received PPDUs410, 420 . If the location field information indicates the firstfrequency band, the OBSS terminal may obtain the SRP for thecorresponding subband from at least one of the first SR field and thesecond SR field. However, if the location field information indicatesthe second frequency band, the OBSS terminal may obtain the SRP for thecorresponding subband from at least one of the third SR field and thefourth SR field.

FIG. 16 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of the trigger-based PPDU according to another embodimentof the present invention. According to the embodiment of FIG. 16 , whenthe total bandwidth on which the trigger-based PPDUs 510 and 520 aretransmitted is 80+80 MHz, the SR fields for the first frequency band maybe set to the same value as the SR fields for the second frequency band.

As described above, STAs transmitting the trigger-based PPDU 510, 520may carry the SRP information obtained from the trigger frame throughthe SR field of the trigger-based PPDU 510, 520. In this case, the STAmay repeatedly insert two pieces of SRP information into the SR fields.For example, the SRP information for each subband obtained from thetrigger frame may be a, b, c and d. a and b may be SRP information forthe first frequency band, and c and d may be SRP information for thesecond frequency band. In this case, a, b, a, and b may be respectivelycontained in the first SR field to the fourth SR field of thetrigger-based PPDU 510 transmitted on the first frequency band. Also, c,d, c, and d may be respectively contained in the first SR field to thefourth SR field of the trigger-based PPDU 520 transmitted on the secondfrequency band. That is, the first SR field and the second SR field forthe first frequency band are respectively set to the same values as thethird SR field and the fourth SR field for the second frequency band. Asdescribed above, the first frequency band and the second frequency bandmay indicate a high (or low) physical frequency band and a low (or high)physical frequency band, respectively. Alternatively, the firstfrequency band and the second frequency band may indicate a band of theP80 channel and a band of the S80 channel, respectively.

An OBSS terminal receiving the trigger-based PPDUs 510, 520 obtains thefirst SRP from at least one of the first SR field and the third SR fieldof the received PPDUs 510, 520. That is, since the information indicatedby the first SR field and the second SR field is the same as theinformation indicated by the third SR field and the fourth SR field, theambiguity of the SR field identification of the OBSS terminal can besolved. According to the embodiment, the SRP information a, b, c, and dtransmitted by the trigger frame can be set in various rules. Accordingto an embodiment, a and b may represent SRPs for the low frequency band,and c and d may represent SRPs for the high frequency band. According toanother embodiment, a and b may represent SRPs for the high frequencyband and c and d may represent SRPs for the low frequency band.According to yet another embodiment, a and b may be set to the samevalues as c and d, respectively.

FIG. 17 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of the trigger-based PPDU according to yet anotherembodiment of the present invention. According to the embodiment of FIG.17 , SR fields for the first frequency band and SR fields for the secondfrequency band may be identified through a physical signaling method.

More specifically, a cyclic shift value of the trigger-based PPDU 610transmitted on the first frequency band may be set differently from acyclic shift value of the trigger-based PPDU 620 transmitted on thesecond frequency band. In this case, the first cyclic shift valueapplied to the first frequency band and the second cyclic shift valueapplied to the second frequency band may be designated in advance.Accordingly, an OBSS terminal receiving the trigger-based PPDU 610 towhich the first cyclic shift value is applied obtains SRP informationfor the corresponding subband from at least one of the first SR fieldand the second SR field of the corresponding PPDU 610. In addition, anOBSS terminal receiving the trigger-based PPDU 620 to which the secondcyclic shift value is applied obtains SRP information for thecorresponding subband from at least one of the third SR field and thefourth SR field of the corresponding PPDU 620.

FIG. 18 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of the trigger-based PPDU according to still anotherembodiment of the present invention. According to the embodiment of FIG.18 , SR fields for the first frequency band and SR fields for the secondfrequency band may be identified through a physical signaling method.

More specifically, a modulation scheme applied to a specific field ofthe trigger-based PPDU 710 transmitted on the first frequency band maybe set differently from a modulation scheme applied to a specific fieldof the trigger-based PPDU 720 transmitted on the second frequency band.In this case, the first modulation scheme applied to the specific fieldtransmitted through the first frequency band and the second modulationscheme applied to the specific field transmitted through the secondfrequency band may be designated in advance. According to an embodimentof the present invention, the specific field to which differentmodulation schemes are applied according to the frequency band may be arepeated L-SIG (RL-SIG).

Accordingly, an OBSS terminal receiving the trigger-based PPDU 710including the RL-SIG to which the first modulation scheme is appliedobtains the SRP information for the corresponding subband from at leastone of the first SR field and the second SR field of the PPDU 710. Inaddition, an OBSS terminal receiving the trigger-based PPDU 720including the RL-SIG to which the second modulation scheme is appliedobtains the SRP information for the corresponding subband from at leastone of the third SR field and the fourth SR field of the PPDU 720.

FIG. 19 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of the trigger-based PPDU according to still yet anotherembodiment of the present invention. According to the embodiment of FIG.19 , the HE-SIG-A of a PPDU in an HE format may contain a non-contiguousband indicator indicating whether the total bandwidth on which the PPDUis transmitted is non-contiguous. Accordingly, whether the totalbandwidth on which the trigger-based PPDU(s) are transmitted iscontiguous 160 MHz or non-contiguous 80+80 MHz can be identified throughthe non-contiguous band indicator.

An OBSS terminal receiving the trigger-based PPDUs 810, 820 maydetermine the SR operation based on the non-contiguous band indicator ofthe received PPDUs 810, 820. If the non-contiguous band indicator is setto 0 (i.e., if the total bandwidth on which the PPDU is transmitted iscontiguous), the OBSS terminal can identify each subband constitutingthe total bandwidth on which the PPDU is transmitted and an SR fieldcorresponding thereto. Accordingly, the OBSS terminal may perform the SRoperation based on the obtained SR field. However, as shown in FIG. 19 ,if the non-contiguous band indicator is set to 1 (i.e., if the totalbandwidth on which the PPDU is transmitted is non-contiguous), the OBSSterminal cannot identify each subband constituting the total bandwidthon which the PPDU is transmitted and an SR field corresponding thereto.Therefore, the OBSS terminal may not perform the above SR operation.

Meanwhile, as described above, in the above embodiments, the firstfrequency band and the second frequency band may indicate a high (orlow) physical frequency band and a low (or high) physical frequencyband, respectively. However, according to another embodiment of thepresent invention, the first frequency band and the second frequencyband may indicate a band of the P80 channel and a band of the S80channel, respectively.

FIGS. 20 and 21 illustrate another embodiment of a method for settingspatial reuse fields of a trigger-based PPDU. As described above, whenthe total bandwidth on which the trigger-based PPDUs are transmitted is160 MHz (or 80+80 MHz), each SR field of the trigger-based PPDU mayindicate an SRP for the individual subband in units of 40 MHz.

According to an embodiment of the present invention, when the totalbandwidth on which the trigger-based PPDU(s) are transmitted is acontiguous frequency band (e.g., 80 MHz, 160 MHz, etc.), the physicalband that constitutes the total bandwidth is determined by apredetermined rule. Thus, an OBSS terminal receiving the trigger-basedPPDU transmitted on a contiguous frequency band can identify thephysical band on which the trigger-based PPDU(s) are transmitted.However, when the total bandwidth on which the trigger-based PPDU(s) aretransmitted consists of non-contiguous frequency bands (e.g., 80+80MHz), the physical bands that constitute the total bandwidth may not bepredetermined. Accordingly, an OBSS terminal receiving the trigger-basedPPDU transmitted on the non-contiguous frequency bands cannot identifywhich frequency band the SR fields of the corresponding PPDU are for.More specifically, when the total bandwidth on which the trigger-basedPPDU(s) are transmitted is 80+80 MHz, the OBSS terminal cannot identifythe set from which the SRP for the subband on which the PPDU is receivedcan be obtained among the first set of SR fields (i.e., at least one ofthe first SR field and the second SR field) and the second set of SRfields (i.e., at least one of the third SR field and the fourth SRfield). Accordingly, when the trigger-based PPDU is transmitted onnon-contiguous frequency bands, there is a need for a method forresolving the ambiguity of the SR field identification of the OBSSterminals receiving it.

FIG. 20 illustrates another embodiment of a method for setting spatialreuse fields of a trigger-based PPDU in order to solve such a problem.According to the embodiment of FIG. 20 , when the total bandwidth onwhich the trigger-based PPDU(s) are transmitted is 80+80 MHz, arepresentative value among SRPs for two 40 MHz bands corresponding toeach other may be set to an SRP for the corresponding bands. Morespecifically, a representative value among the SRP for the first 40 MHzband and the SRP for the third 40 MHz band may be used as the first SRPfor the first 40 MHz band and the third 40 MHz band. Thus, the first SRfield and the third SR field of the trigger-based PPDU represent thesame representative value. Likewise, a representative value among theSRP for the second 40 MHz band and the SRP for the fourth 40 MHz bandmay be used as the second SRP for the second 40 MHz band and the fourth40 MHz band. Thus, the second SR field and the fourth SR field of thetrigger-based PPDU represent the same representative value. In thiscase, the first 40 MHz band and the second 40 MHz band constitute thefirst frequency band on which the trigger-based PPDU(s) are transmitted,and the third 40 MHz band and the fourth 40 MHz band constitute thesecond frequency band on which the trigger-based PPDU(s) aretransmitted. According to the embodiment of the present invention, asmaller value among the plurality of SRPs may be set as a representativevalue of the corresponding SRPs.

An OBSS terminal receiving the trigger-based PPDU having a totalbandwidth of 80+80 MHz may obtain the first SRP from at least one of thefirst SR field and the third SR field of the received PPDU, and mayobtain the second SRP from at least one of the second SR field and thefourth SR field of the received PPDU. That is, since the informationindicated by the first SR field and the second SR field is the same asthe information indicated by the third SR field and the fourth SR field,the ambiguity of the SR field identification of the OBSS terminal can besolved.

On the other hand, when the total bandwidth on which the trigger-basedPPDU(s) are transmitted is 160 MHz, each SR field may indicate an SRPfor the different subbands in 40 MHz units. That is, the first SR fieldindicates the SRP for the first 40 MHz band, the second SR fieldindicates the SRP for the second 40 MHz band, the third SR fieldindicates the SRP for the third 40 MHz band, and the fourth SR fieldindicates the SRP for the fourth 40 MHz band. In this case, the first 40MHz band to the fourth 40 MHz band constitute the total bandwidth 160MHz on which the trigger-based PPDU(s) are transmitted. As such, byallowing the SR fields of the trigger-based PPDU transmitted oncontiguous frequency band to indicate SRPs for individual subbands, anSR operation that is more suitable for individual subbands can beperformed.

FIG. 21 illustrates yet another embodiment of a method for setting andusing spatial reuse fields of a trigger-based PPDU. According to theembodiment of FIG. 21 , each SR field of the trigger-based PPDU mayindicate an SRP for different subbands, and an OBSS terminal receivingthe PPDU may select an SRP for the SR operation of the correspondingsubband among SRPs indicated by a plurality of SR fields.

More specifically, even if the total bandwidth on which thetrigger-based PPDU(s) are transmitted is 80+80 MHz, each SR field mayindicate an SRP for the different subbands in units of 40 MHz. That is,the first SR field indicates the SRP for the first 40 MHz band, thesecond SR field indicates the SRP for the second 40 MHz band, the thirdSR field indicates the SRP for the third 40 MHz band, and the fourth SRfield indicates the SRP for the fourth 40 MHz band. In this case, thefirst 40 MHz band and the second 40 MHz band constitute the firstfrequency band on which the trigger-based PPDU(s) are transmitted, andthe third 40 MHz band and the fourth 40 MHz band constitute the secondfrequency band on which the trigger-based PPDU(s) are transmitted.

An OBSS terminal receiving the trigger-based PPDU having a totalbandwidth of 80+80 MHz uses a smaller value between the two SR fieldscorresponding to each other as an SRP for the corresponding subband.That is, the smaller value between the first SR field value and thethird SR field value is used for the SRP for the first 40 MHz bandand/or the third 40 MHz band. In addition, the smaller value between thesecond SR field value and the fourth SR field value is used for the SRPfor the second 40 MHz band and/or the fourth 40 MHz band.

FIG. 22 illustrates a method for configuring an HE-SIG-A and spatialreuse fields of a trigger-based PPDU according to a further embodimentof the present invention. According to the embodiment of FIG. 22 , inorder to solve the ambiguity of the SR field identification of the OBSSterminal described above, the SR operation may be restricted in thetrigger-based PPDU transmitted on the non-contiguous frequency bands.More specifically, the SR fields of the trigger-based PPDUs 910, 920transmitted on the 80+80 MHz band may indicate a predetermined value notallowing the SR operation. To this end, the AP may carry an SRPindicating a predetermined value not allowing the SR operation throughthe trigger frame.

FIG. 23 illustrates a method for signaling spatial reuse fields of atrigger-based PPDU according to another embodiment of the presentinvention. According to the embodiment of FIG. 23 , when the totalbandwidth indicated by the bandwidth field of the trigger-based PPDU is80+80 MHz or 160 MHz, the SR field may indicate an SRP for a subband of20 MHz bandwidth. In the embodiment of FIG. 23 , when the totalbandwidth on which the trigger-based PPDU(s) are transmitted is 20 MHz,40 MHz, or 80 MHz, the value indicated by each SR field is the same asthat illustrated in FIG. 13 .

According to the embodiment of FIG. 23 , when the total bandwidth onwhich the trigger-based PPDU(s) are transmitted is 160 MHz (or 80+80MHz), the values of the SR fields for the first 80 MHz frequency bandmay be set different from the values of the SR fields for the second 80MHz frequency band. That is, the first SR field to the fourth SR fieldof the trigger-based PPDU transmitted on the first frequency bandrespectively indicate SRPs for the first 20 MHz band to the fourth 20MHz band of the first frequency band. In addition, the first SR field tothe fourth SR field of the trigger-based PPDU transmitted on the secondfrequency band respectively indicate SRPs for the first 20 MHz band tothe fourth 20 MHz band of the second frequency band. In this case, thefirst SR field to the fourth SR field for the first frequency band andthe first SR field to the fourth SR field for the second frequency bandmay be determined independently from each other.

Thus, to indicate the SRP in units of 20 MHz in a total bandwidth of 160MHz (or 80+80 MHz), a maximum of eight SRPs should be carried in thetrigger frame. Therefore, the length of the trigger frame may bedetermined to be variable according to the total bandwidth information.That is, if the total bandwidth is 20 MHz, 40 MHz, or 80 MHz, thetrigger frame carries a total of 16 bits of SRP, and if the totalbandwidth is 160 MHz (or 80+80 MHz), the trigger frame carries a totalof 32 bits of SRP.

FIG. 24 illustrates a method for signaling a bandwidth field accordingto an embodiment of the present invention. In the embodiments describedabove, it may be necessary to identify whether the total bandwidth onwhich the trigger-based PPDU(s) are transmitted is contiguous 160 MHz ornon-contiguous 80+80 MHz. According to the embodiment of the presentinvention, whether or not the total bandwidth of the transmitted PPDU iscontiguous may be signaled via the HE-SIG-A.

According to an embodiment of the present invention, as described abovewith reference to FIG. 19 , the HE-SIG-A of a PPDU in an HE format maycontain a non-contiguous band indicator. Thus, whether the totalbandwidth on which the trigger-based PPDU(s) are transmitted iscontiguous 160 MHz or non-contiguous 80+80 MHz can be identified throughthe non-contiguous band indicator.

According to another embodiment of the present invention, whether thetotal bandwidth of the transmitted PPDU is contiguous may be signaledthrough the bandwidth field of the HE-SIG-A as shown in FIG. 24 . Morespecifically, the non-contiguous bandwidth may be indicated via apredetermined index of the bandwidth field of the HE-SIG-A. For example,the indices 0, 1, 2, and 3 of the bandwidth field may represent 20 MHz,40 MHz, 80 MHz, and 160 MHz, respectively. In addition, the index 4 ofthe bandwidth field may represent non-contiguous 80+80 MHz. When thebandwidth field of the trigger-based PPDU indicates contiguous 160 MHz,an OBSS terminal receiving the PPDU may perform an SR operation for 160MHz. However, when the bandwidth field of the trigger-based PPDUindicates non-contiguous 80+80 MHz, the OBSS terminal may perform an SRoperation for 80 MHz including the subband on which the correspondingPPDU is received.

According to yet another embodiment of the present invention, whetherthe total bandwidth of the transmitted PPDU is contiguous may beidentified according to whether the corresponding SR fields are set tothe same value. For example, when the bandwidth field of thetrigger-based PPDU indicates 160 MHz, and the first SR field and thesecond SR field are set to the same values as the third SR field and thefourth SR field, respectively, the total bandwidth on which thetrigger-based PPDU(s) are transmitted may be identified as 80+80 MHz.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

Industrial Applicability

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1-20. (canceled)
 21. A wireless communication terminal, the terminalcomprising: a processor; and a communication unit, wherein the processoris configured to: receive a trigger frame soliciting uplink multi-usertransmission, and transmit a trigger-based physical protocol dataunit(PPDU) including a bandwidth field and a plurality of spatial reusefields in respond to the trigger frame, wherein the bandwidth fieldindicates a bandwidth related to transmission and reception of thetrigger-based PPDU, and wherein a frequency band in which the pluralityof spatial reuse fields is applied and spatial reuse parameters of theplurality of spatial reuse fields vary according to a size of thebandwidth indicated by the bandwidth field.
 22. The wirelesscommunication terminal of claim 21, wherein the frequency band to whicheach of the plurality of spatial reuse fields is applied is 20 MHz whenthe bandwidth field indicates 20 MHz or 40 MHz.
 23. The wirelesscommunication terminal of claim 21, wherein the plurality of spatialreuse fields includes a first spatial reuse field and a second spatialreuse field, and wherein a value of the first spatial reuse field is setequal to a value of the second spatial reuse field.
 24. The wirelesscommunication terminal of claim 21, wherein each of the plurality ofspatial reuse fields includes a spatial reuse parameter for a spatialreuse operation of an overlapping basic service set (OBSS) terminal. 25.The wireless communication terminal of claim 21, wherein the pluralityof spatial reuse fields includes a first spatial reuse field and asecond spatial reuse field, and wherein the first spatial reuse fieldindicates a spatial reuse parameter for the first 80 MHz, and the secondspatial reuse field indicates a spatial reuse parameter for the second80 MHz when the bandwidth field indicates 160 MHz.
 26. A wirelesscommunication method of a wireless communication terminal, the methodcomprising: receiving a trigger frame soliciting uplink multi-usertransmission; and transmitting a trigger-based physical protocol dataunit(PPDU) including a bandwidth field and a plurality of spatial reusefields in respond to the trigger frame, wherein the bandwidth fieldindicates a bandwidth related to transmission and reception of thetrigger-based PPDU, and wherein a frequency band in which the pluralityof spatial reuse fields is applied and spatial reuse parameters of theplurality of spatial reuse fields vary according to a size of thebandwidth indicated by the bandwidth field.
 27. The wirelesscommunication terminal of claim 26, wherein the frequency band to whicheach of the plurality of spatial reuse fields is applied is 20 MHz whenthe bandwidth field indicates 20 MHz or 40 MHz.
 28. The wirelesscommunication terminal of claim 26, wherein the plurality of spatialreuse fields includes a first spatial reuse field and a second spatialreuse field, and wherein a value of the first spatial reuse field is setequal to a value of the second spatial reuse field.
 29. The wirelesscommunication terminal of claim 26, wherein each of the plurality ofspatial reuse fields includes a spatial reuse parameter for a spatialreuse operation of an overlapping basic service set (OBSS) terminal. 30.The wireless communication terminal of claim 26, wherein the pluralityof spatial reuse fields includes a first spatial reuse field and asecond spatial reuse field, and wherein the first spatial reuse fieldindicates a spatial reuse parameter for the first 80 MHz, and the secondspatial reuse field indicates a spatial reuse parameter for the second80 MHz when the bandwidth field indicates 160 MHz.